Cables with Bend Insensitive Optical Fibers

ABSTRACT

Fiber optic cables and methods of manufacturing fiber optic cables are disclosed herein. According to one embodiment, a fiber optic cable includes a plurality of optical fibers having a lay length of greater than 160 mm. The fiber optic cable also includes strength material surrounding the plurality of optical fibers and a polymer jacket surrounding the strength material. Each of the optical fibers is configured to exhibit a bend-induced optical attenuation of less than or equal to about 0.6 dB when wrapped one turn around a 7.5 mm mandrel.

BACKGROUND

The present disclosure generally relates to fiber optic cables andmethods of manufacturing fiber optic cables.

The science of fiber optics is applicable to various fields oftechnology and is often used for the transmission of communicationsignals. Individual optical fibers, which each act as a waveguide fordirecting light from one end of the fiber to the other, can be bundledtogether to form a fiber optic cable.

Fiber optic cable can be installed outdoors over long distances, eitherunderground or above ground, and can also be installed within buildings.When installed indoors, fiber optic cable may be run through the plenumspaces of buildings alongside HVAC equipment and other utilities. Fiberoptic cable may also be run through riser spaces, such as elevatorshafts or other spaces within a building.

When installing indoor-type fiber optic cable, it may be necessary attimes to bend the cable around corners or other structures in abuilding. A bent fiber optic cable may cause the light within itsoptical fibers to be scattered or lost when the bend radius is toosmall. The scattering or loss of light is referred to herein as opticalattenuation.

Stranding the optical fibers in a fiber optic cable is one way to reduceoptical attenuation caused by bending a cable. However, the speed atwhich a fiber optic cable is manufactured may be limited by thestranding.

SUMMARY

The present disclosure describes fiber optic cables and methods ofmanufacturing fiber optic cables. According to some embodimentsdisclosed herein, a fiber optic cable may include a group of opticalfibers that may not be stranded or may be stranded (e.g., twisted) witha lay length of greater than or equal to about 160 mm. The fiber opticcable may also include strength material surrounding the group ofoptical fibers, and an extruded polymer jacket surrounding the strengthmaterial. The jacket may tightly surround the strength material. Each ofthe optical fibers (e.g., in isolation) may be configured to exhibit abend-induced optical delta attenuation of less than or equal to about0.6 dB when wrapped one turn around a 7.5 mm mandrel.

In some implementations, a method of manufacturing a fiber optic cablecomprises stranding a group of optical fibers with a lay length ofgreater than or equal to about 160 mm. Each optical fiber (e.g., inisolation) may be configured to exhibit a bend-induced attenuation ofless than or equal to about 0.6 dB when wrapped one turn around a 7.5 mmmandrel. The method may also include surrounding the plurality ofoptical fibers with a strength member and extruding a polymer jacketaround the strength member.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments, andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The components of the following figures are illustrated to emphasize thegeneral principles of the present disclosure and are not necessarilydrawn to scale. Reference characters designating correspondingcomponents are repeated as necessary throughout the figures for the sakeof consistency and clarity.

FIG. 1 is a schematic cross-sectional view of a fiber optic cableaccording to a first embodiment of this disclosure, wherein the crosssection is perpendicular to the length of the fiber optic cable.

FIG. 2 is an isolated, schematic side view of an indeterminate length ofstranded optical fibers of the cable of FIG. 1.

FIG. 3 is an isolated, schematic cross-sectional view of a lowattenuation optical fiber of the optical fibers of FIGS. 1 and 2,wherein the cross section is perpendicular to the length of the lowattenuation optical fiber.

FIG. 4 is a graph illustrating the refractive indices of the differentconcentric layers of the low attenuation optical fiber of FIG. 3.

FIG. 5 is a schematic cross-sectional view of a fiber optic cableaccording to a second embodiment of this disclosure, wherein the crosssection is perpendicular to the length of the fiber optic cable.

FIG. 6 is a chart illustrating differences between the intrinsic opticalattenuation of different types of optical fibers stranded in atightly-jacketed comparative cable that is in some ways similar to thecable of FIG. 3.

FIG. 7 is a chart illustrating changes in optical attenuation that occurwhen the tightly-jacketed comparative cable is wrapped.

DETAILED DESCRIPTION

Some aspects of the present disclosure are directed to fiber opticcables containing a plurality of low attenuation optical fibers, andmethods of manufacturing the fiber optic cables. According to variousembodiments, the fiber optic cables described herein may include aplurality of optical fibers arranged with little or no stranding ortwisting around each other. Strength members (e.g., aramid or othersuitable materials), which may be used for strengthening and to protectthe optical fibers, can also be arranged with little or no stranding. Inaccordance with one aspect of this disclosure, the optical fibers andstrength members may be substantially parallel to each other along alength of cable.

FIG. 1 is a schematic cross-sectional view of a fiber optic cable 24according to a first embodiment of this disclosure. The cable 24includes a group of optical fibers 26 that may not be stranded, or maybe stranded with a lay length, such as but not limited to a long laylength, as will be discussed in greater detail below. FIG. 2 is anisolated, schematic side view of an indeterminate length of the group ofoptical fibers 26 stranded with a lay length, as will be discussed ingreater detail below.

In accordance with the first embodiment and as shown in FIG. 1, strengthmaterial 28 surrounds the group of optical fibers 26, and a jacket 32surrounds the strength material 28 and a ripcord 30. The strengthmaterial 28 is in a space between the group of optical fibers 26 and thejacket 32. The strength material 28 allows the optical fibers to move toa limited extent within the jacket 32. In accordance with the firstembodiment, the strength material 28 may be, or may include, aramidstrands that extend along the length of the cable 24, and the aramidstrands may be stranded or not stranded. In some embodiments, thestrength material 28 not only surrounds the group of optical fibers 26but may also be positioned in the middle of the group of optical fibersoptical fibers 26, as schematically shown in FIG. 1. Other arrangementsand other types of strength material 28 are within the scope of thisdisclosure.

In accordance with the version of the first embodiment shown in FIGS. 1and 2, the group of optical fibers 26 includes six optical fibersarranged in a circular pattern, namely a first optical fiber 12, asecond optical fiber 14, a third optical fiber 16, a fourth opticalfiber 18, a fifth optical fiber 20, and a sixth optical fiber 22. InFIG. 2, a visible portion of the first optical fiber 12 is illustratedin a darkened manner to highlight this particular fiber. Hidden portionsof the first optical fiber 12 are shown in dashed lines. A dimensionreferred to as lay length, which is designated by the distance L in FIG.2, represents a measurement of the distance measured along the length ofthe central axis of the group of optical fibers 26 in which the opticalfibers 12, 14, 16, 18, 20, 22 complete one revolution around the centralaxis. As illustrated in FIG. 2, the lay length L is measured for adistance of one revolution of the first optical fiber 12 from one peaklocation to its next peak location.

When the group of optical fibers 26 are stranded, it is typically S-Zstranded (i.e., twisted), such that, along the length of the cable 24,the direction of twist changes from one direction, i.e., the “S”direction, to the opposite direction, i.e., the “Z” direction, andcontinues to alternate between these two directions along the length ofthe cable 24.

Whereas the group of optical fibers 26 is shown as being stranded inFIG. 2, the group of optical fibers 26 is not required to be stranded.That is and in accordance with the first embodiment of this disclosure,the lay length of the group of optical fibers 26 may be in a range thatextends to infinity (i.e., in some versions of the first embodiment thegroup of optical fibers 26 are not stranded). In accordance with oneaspect of the first embodiment, each of the optical fibers of the groupof optical fibers 26 (e.g., the optical fibers 12, 14, 16, 18, 20, 22)may be characterized as being “substantially parallel” to one anotherand/or the longitudinal axis of the cable when they have a relativelylong lay length or are not stranded, as will be discussed in greaterdetail below. Similar to the group of optical fibers 26, the strengthmaterial 28 (e.g., aramid strands) may be stranded or not stranded.

More specifically and in accordance with the first embodiment of thisdisclosure, the group of optical fibers 26 (e.g., each of the opticalfibers 12, 14, 16, 18, 20, 22) may have a lay length L of greater thanor equal to about 160 mm, greater than or equal to about 250 mm, greaterthan or equal to about 500 mm, or greater than or equal to about 1000 mmor more. For each of the foregoing ranges of the lay length L of thegroup of optical fibers, the upper end of the range may be infinity(e.g., the group of optical fibers 26 may not be stranded).

Also in accordance with the first embodiment, the strength material 28or strength members (e.g., aramid strands or fibers) may be arrangedaround the group of optical fibers 26 with a lay length of greater thanor equal to about 130 mm, greater than or equal to about 250 mm, greaterthan or equal to about 500 mm, or even greater than or equal to about1000 mm. For each of the foregoing ranges of lay length L of thestrength material, the upper end of the range may be infinity (e.g., thestrength material 28 may not be stranded).

The lay length of the strength members of the strength material 28 maybe about the same as the lay length of the optical fibers 26.Alternatively, the lay length of the strength members of the strengthmaterial 28 may be in a range from about half the lay length of theoptical fibers 26 to about twice the lay length of the optical fibers26. For example, if the optical fibers 26 have a lay length of about 300mm, the lay length of the strength members of the strength material 28may range from about 150 mm to about 600 mm. In one embodiment, the laylength of the optical fibers 26 is about 250 mm and the lay length ofthe strength members of the strength material 28 is about 350 mm.

The specific lay lengths mentioned herein may depend on the type ofcable being manufactured and any specific details in the design of thecable. For example, the lay lengths may be applicable when the group ofoptical fibers 26 includes single mode optical fibers and/or multimodeoptical fibers. The lay length for the strength material 28 may be aboutthe same as the lay length of the group of optical fibers 26, or theselay lengths may vary. For example, the lay length of the strengthmaterial that surrounds the group of optical fibers 26 may be greaterthan any lay length of the group of optical fibers 26.

In accordance with the first embodiment, each of the optical fibers 12,14, 16, 18, 20, 22 exhibits relatively low attenuation. The lowattenuation of the optical fibers 12, 14, 16, 18, 20, 22 may include lowintrinsic attenuation and/or low delta attenuation. Intrinsicattenuation refers to optical attenuation exhibited under low stressconditions, such as the attenuation over 1 km of straight opticalfiber/cable. For example, each of the optical fibers 12, 14, 16, 18, 20,22 may have an intrinsic attenuation of less than or equal to about 3.0dB/km.

Delta attenuation refers to optical attenuation exhibited when theoptical fiber/cable is subjected to certain stress conditions, such ascrushing forces, bending forces, tensile forces, bend performance tests,crush performance tests, or tensile tests. As an example for deltaattenuation, for each of the optical fibers 12, 14, 16, 18, 20, 22 inisolation, when wrapped one turn around a 7.5 mm mandrel, the opticalfiber may have a delta attenuation of less than or equal to about 0.6dB, less than or equal to about 0.2 dB, or less than or equal to about0.08 dB.

In accordance with the first embodiment, each of the optical fibers 12,14, 16, 18, 20, 22 is a tight buffered low attenuation optical fiber. Inone specific example, the low attenuation optical fibers 12, 14, 16, 18,20, 22 may be ClearCurve® brand multimode optical fibers, or morespecifically tight buffered ClearCurve® brand multimode optical fibers,available from Corning Cable Systems of Hickory, N.C., and Corning Inc.,of Corning, N.Y., although other suitable optical fibers may be used,such as ClearCurve® brand single mode optical fibers.

As schematically shown in FIG. 1, each of the tight buffered lowattenuation optical fibers 12, 14, 16, 18, 20, 22 includes a tightbuffer extending around a low attenuation optical fiber. For each of theoptical fibers 12, 14, 16, 18, 20, 22, the tight buffer is typically asubstantially cylindrical, outer extrusion of polymeric material (e.g.,PVC) that extends substantially coaxially around and is fixedlyconnected to the central low attenuation optical fiber.

FIG. 3 is an isolated, schematic cross-sectional view of the lowattenuation optical fiber 12 without its outer tight buffer, or showingthe outer tight buffer with a reduced thickness, in accordance with thefirst embodiment. In accordance with the first embodiment, the followingdiscussion of the low attenuation optical fiber 12 is applicable to eachof the other optical fibers 14, 16, 18, 20, 22. Whereas a specificexample of a suitable low attenuation optical fiber 12 is described inthe following, any other suitable optical fibers may be used.

The low attenuation optical fiber 12 includes a core 44 and a cladding46 that surrounds and is directly adjacent to the core 44. The cladding46 includes an inner layer 48, a middle layer 50, and an outer layer 52.In some embodiments, the cladding 46 may have an overall radius of about125 μm.

Generally, the index of refraction of the core 44 is graded from a highindex of refraction at a central point to a medium index at an outerpoint. For example, the core 44 may comprise a graded glass or othersuitable material for radially varying the index of refraction. Theinner layer 48 includes a medium index of refraction, the middle layer50 includes a low or depressed index or refraction, and the outer layer52 includes a medium index of refraction. To achieve a low index ofrefraction, the middle layer 50 may comprise, for example, fluorine,boron, combinations of fluorine and boron, glass having a plurality ofvoids, glass doped with one or more down-dopants, such as fluorine,boron, or mixtures thereof, or other compositions or mixtures. In someembodiments, the depressed-index of the middle layer 50 of the cladding46 may be spaced apart from the core 44 by the inner layer 48.

The middle layer 50 may have a width of at least about 1 μm and maycomprise a substantially consistent material composition throughout,such that its refractive index may vary by less than about 0.2% acrossits width. The middle layer 50 may be spaced from the core 44 by theinner layer 48 or other suitable gap of at least about 0.5 μm.Therefore, the width of the inner layer 48 may be at least about 0.5 μm.

To achieve a low attenuation, the core 44 may be configured with arelatively high index of refraction, the inner layer 48 may beconfigured with a medium index of refraction, the middle layer 50 may beconfigured with a relatively low index of refraction, and the outerlayer 52 may be configured with a medium index of refraction. Thecomposition of the low attenuation optical fibers 12 exhibits a lowamount of intrinsic optical attenuation and a low amount of deltaattenuation even when bent.

The core 44 may have a graded index of refraction in which the index ofrefraction varies in a gradual, linear, exponential, or other mannerfrom a centermost portion of the core 44 to an outermost portion of thecore 44. In some implementations, the refractive index profile of thecore 44 can have a parabolic or other curved shape. The middle layer 50of the cladding 46 may comprise a refractive index relatively depressedcompared with the inner layer 48 and outer layer 52 of the cladding 46.Also, the depressed-index middle layer 50 may have a refractive indexdelta less than about 0.2% along its width when its width is at leastabout 1 μm.

In some embodiments, the low attenuation optical fiber 12 may beconstructed as a single-mode fiber (SMF), which limits the light thatcan enter the fiber to a single mode (or self-consistent electric fielddistribution). As an example, the core 44 of an SMF may have a diameterof about 8-9 μm. In some embodiments, the low attenuation optical fiber12 may be constructed as a multi-mode fiber (MMF), which receives lightfrom multiple angles to allow multiple modes of light. As an example,the core 44 of a MMF may have a diameter of about 50 μm, 62.5 μm, 100μm, or other suitable diameter. For MMF, the diameter of the core 44 ofthe low attenuation optical fiber 12 may be about 50 μm.

In some embodiments, the cladding 46 may contain voids. The voidsaccording to various implementations may be non-periodically or randomlylocated within the middle layer 50. Also, the size, shape, anddistribution of the voids may be variable. In some embodiments, thevoids may extend less than one meter along the length of the lowattenuation optical fiber 12.

The low attenuation optical fiber 12 disclosed herein exhibits very lowbend-induced optical attenuation, in particular very low macro-bendinginduced optical attenuation. In some embodiments, high bandwidth isprovided by low maximum relative refractive index in the core 44, andlow bend losses are also provided.

The low attenuation optical fiber 12 may further exhibit a one-turn, 10mm diameter mandrel wrap optical attenuation increase of less than orequal to about 0.4 dB/turn at 850 nm, a numerical aperture (NA) ofgreater than 0.14, greater than 0.17, greater than 0.18, or even greaterthan 0.185, and an overfilled bandwidth greater than 1.5 GHz-km at 850nm.

The core 44 may be configured to provide an overfilled (OFL) bandwidthof greater than 1.5 GHz-km, greater than 2.0 GHz-km, greater than 3.0GHz-km, or even greater than 4.0 GHz-km at an 850 nm wavelength. Thesehigh bandwidths can be achieved while still maintaining a one-turn, 10mm diameter mandrel wrap optical attenuation increase at an 850 nmwavelength of less than 0.5 dB, less than 0.3 dB, less than 0.2 dB, oreven less than 0.15 dB. These high bandwidths can also be achieved whilealso maintaining a one-turn, 20 mm diameter mandrel wrap opticalattenuation increase at an 850 nm wavelength of less than 0.2 dB, lessthan 0.1 dB, or even less than 0.05 dB, and a one-turn, 15 mm diametermandrel wrap optical attenuation increase at an 850 nm wavelength, ofless than 0.2 dB, less than 0.1 dB, or even less than 0.05 dB.

The low attenuation optical fiber 12 is further capable of providing anumerical aperture (NA) greater than 0.17, greater than 0.18, or evengreater than 0.185. The low attenuation optical fiber 12 is furthersimultaneously capable of exhibiting an OFL bandwidth at 1300 nm whichis greater than about 500 MHz-km, greater than about 600 MHz-km, or evengreater than about 700 MHz-km. Such low attenuation optical fiber 12 arefurther simultaneously capable of exhibiting minimum calculatedeffective modal bandwidth (Min EMBc) of greater than about 1.5 MHz-km,greater than about 1.8 MHz-km, or even greater than about 2.0 MHz-km at850 nm.

When configured as a MMF, the low attenuation optical fiber 12 disclosedherein exhibits a spectral optical attenuation of less than 3 dB/km at850 nm, less than 2.5 dB/km at 850 nm, less than 2.4 dB/km at 850 nm, oreven less than 2.3 dB/km at 850 nm. The MMF fibers disclosed hereinexhibit a spectral optical attenuation of less than 1.0 dB/km at 1300nm, less than 0.8 dB/km at 1300 nm, or even less than 0.6 dB/km at 1300nm. In some embodiments, the NA of the low attenuation optical fiber 12is less than 0.23 and greater than 0.17 or even greater than 0.18, oreven less than 0.215 and greater than 0.185.

FIG. 4 is a graph 56 illustrating a schematic representation of arefractive index profile of the concentric layers of the low attenuationoptical fiber 12 shown in FIG. 3, in accordance with the firstembodiment. The graph 56 shows the index of refraction of the lowattenuation optical fiber 12 at different radii from a central point ofthe low attenuation optical fiber 12. A first radius R₁ represents thecore 44, a second radius R₂ extends to the outer surface of the innerlayer 48 of the cladding 46, and so on. The portion of the graph 56representing the index of refraction of the core 44 is referenced as441, the portion of the graph representing the index of refraction ofthe inner cladding layer 48 is referenced as 481, and so on.

As illustrated, the depressed-index middle layer 501 is offset from thecore 441 and is surrounded by outer layers 481 and 521. In someembodiments, the core 44 extends radially outwardly from a centerline toa radius R1, wherein 10≦R1≦40 μm, or 20≦R1≦40 μm. In some embodiments,22≦R1≦34 μm. In some embodiments, the radius of the core 44 is betweenabout 22 to 28 μm. In some embodiments, the radius of the core 44 isbetween about 28 to 34 μm.

In some embodiments, the core has a maximum relative refractive indexdelta less than or equal to 1.2% and greater than 0.5% or even greaterthan 0.8%. In other embodiments, the core has a maximum relativerefractive index delta less than or equal to 1.1% and greater than 0.9%.

In some embodiments, the optical fiber 12 exhibits a 1 turn, 10 mmdiameter mandrel optical attenuation increase of no more than 1.0 dB, nomore than 0.6 dB, no more than 0.4 dB, no more than 0.2 dB, or even nomore than 0.1 dB, at all wavelengths between 800 nm and 1400 nm.

Referring again to FIG. 4, the core 44 and cladding 46 may contain glassor other suitable optically transparent material. The core 44 has radiusR₁ and a maximum refractive index delta Δ1MAX. The inner layer 48 haswidth W2 (equal to R₂-R₁) and outer radius R₂. Middle layer 50 has aminimum refractive index delta percent Δ3MIN, width W3 (equal to R₃-R₂)and outer radius R₃. As illustrated, the middle layer 50 is offset orspaced away from the core 44 by the inner layer 48. The middle layer 50surrounds and contacts the inner layer 48. The outer layer 52 surroundsand contacts the middle layer 50.

As best understood with reference to FIG. 3, the cladding 46 issurrounded by at least one coating 54, which may in some embodimentscomprise a low modulus primary coating and a high modulus secondarycoating. The coating 54 is typically surrounded by the tight buffer (notshown in FIG. 3) that is typically an outermost extrusion of polymericmaterial (e.g., PVC) that extends around and is fixedly connected to thecoating 54. Alternatively, the coating 54 may be thicker than shown inFIG. 3, such that the coating is the outermost tight buffer. That is,the coating 54 may be characterized as schematically illustrating theoutermost tight buffer. The outermost tight buffer typically has anouter diameter of about 0.9 mm.

In some embodiments, the inner layer 48 has a refractive index profileΔ2(r) with a maximum relative refractive index Δ2MAX, and a minimumrelative refractive index Δ2MIN, and in some embodiments Δ2MAX=Δ2MIN.The depressed-index layer 50 has a refractive index profile Δ3(r) with aminimum relative refractive index Δ3MIN. The outer layer 52 has arefractive index profile Δ4(r) with a maximum relative refractive indexΔ4MAX, and a minimum relative refractive index Δ4MIN, where in someembodiments Δ4MAX=Δ4MIN. In some embodiments, Δ1MAX>Δ2MAX>Δ3MIN. In someembodiments, the inner layer 48 has a substantially constant refractiveindex profile with a constant Δ2(r); in some embodiments, Δ2(r)=0%. Theouter layer 52 may have a substantially constant refractive indexprofile, with a constant Δ4(r); in some of these embodiments, Δ4(r)=0%.

The core 44 may have an entirely positive refractive index profile,where Δ1(r)>0%. R1 is defined as the radius at which the refractiveindex delta of the core 44 first reaches a value of 0.05% or othervalue, going radially outwardly from the centerline. In someembodiments, the core 44 contains little or no fluorine. In someembodiments, the inner layer 48 may have a relative refractive indexprofile Δ2(r) having a maximum absolute magnitude less than 0.05%, andΔ2MAX<0.05% and Δ2MIN>−0.05%, and the depressed-index layer 50 beginswhere the relative refractive index of the cladding first reaches avalue of less than −0.05%, going radially outwardly from the centerline.In some embodiments, the outer layer 52 has a relative refractive indexprofile Δ4(r) having a maximum absolute magnitude less than 0.05%, andΔ4MAX<0.05% and Δ4MIN>−0.05%, and the depressed-index layer 50 endswhere the relative refractive index of the cladding first reaches avalue of greater than −0.05%, going radially outwardly from the radiuswhere Δ3MIN is found.

Examples of methods for manufacturing cable 24 are described in thefollowing, in accordance with the first embodiment of this disclosure.Initially, the optical fibers 12, 14, 16, 18, 20, 22 may be broughttogether to form the group of optical fibers 26. For example, theoptical fibers 12, 14, 16, 18, 20, 22 may be stranded together with alay length (e.g., a lay length of greater than or equal to about 160 mm,greater than or equal to 250 mm, greater than or equal to 500 mm, orgreater than or equal to about 1000 mm or more). As another example, theoptical fibers 12, 14, 16, 18, 20, 22 may be stranded together with alay length that approaches infinity, so that they are in a substantiallyparallel arrangement with one another. Any stranding of the group ofoptical fibers 26 may be done around a central portion or part of thestrength material 28 (e.g., a central strength member). As still anotherexample, the optical fibers 12, 14, 16, 18, 20, 22 may be broughttogether so that they are not stranded together, so that they are in asubstantially parallel arrangement with one another.

The group of optical fibers 26 may be surrounded with the strengthmaterial 28 (e.g., the outer portion of the strength material), such asby stranding the strength material around the group of optical fibers.For example, the strength material 28 may be stranded around the groupof optical fibers 26 with a lay length (e.g., the strength material 28may have a lay length of greater than or equal to about 130 mm, greaterthan or equal to about 250 mm, greater than or equal to about 500 mm, oreven greater than or equal to about 1000 mm). As another example, thestrength material 28 may be stranded around the group of optical fibers26 with a lay length that approaches infinity, so that the strengthmembers are in a substantially parallel arrangement with one another. Asstill another example, strength material 28 may be arranged around thegroup of optical fibers 26 in a manner such that the strength materialis not stranded, so that the strength members are in a substantiallyparallel arrangement with one another.

The polymeric jacket 31 is typically extruded around the strength member28. Any suitable jacket 31 may be used. For example, the jacket 32 maybe configured to meet certain standards, fire codes, burn codes, orother regulations, such as those for defining the acceptable materialsand construction of fiber optic cables for use in plenum spaces or riserspaces. The jacket 31 may include or consist essentially of a polymermaterial that meets burn rating standards for low-smoke zero-hydrogen(LSZH). The rip cord 30 may be optional. If the rip cord 30 is included,typically the polymeric jacket 31 is extruded around the rip cord sothat the rip cord is adjacent the inner surface of the jacket.

In accordance with one aspect of the first embodiment, production speedmay be increased by arranging the optical fibers 12, 14, 16, 18, 20, 22and the strength members of the strength material 28 substantially inparallel with one another. Usually, the line speed (i.e., the speed atwhich the optical fibers, strength material and other materials arejoined together to form a cable) is limited by the rotational speed ofstranding machinery used to strand the optical fibers and strengthmaterial. In accordance with one aspect of the first embodiment, a cable(e.g., the cable 24) with a greater lay length (e.g., of the opticalfibers and strength material) may be manufactured more quickly becausethere is less stranding to be performed.

Sometimes the line speed is limited by the aramid server, which feedsthe aramid material (e.g., the strength material 28) to the cable. Somearamid servers can run at speeds of up to about 120 RPM. If the laylength of the aramid strength material 28 is about 250 mm, the cable canbe manufactured at about 30 meters per minute. If the lay length of thearamid strength material 28 is 1000 mm, for example, the line speed maybe about 120 meters per minute—a fourfold increase in production.

Examples of methods of using the cable 24 are discussed in thefollowing, in accordance with the first embodiment of this disclosure.When the cable 24 is installed, it may be bent. For example, the cable24 may tolerate bending to a bend radius of at least about five times,or at least about three times, the diameter of the fiber optic cablewithout significant optical attenuation. The substantially parallelarrangement of the optical fibers of the optical fibers 26 may help toreduce optical attention when the optical cable 24 is bent by allowingthe optical fibers to move into a somewhat flattened arrangement, suchthat each fiber exerts relatively less crushing forces to the otheroptical fibers.

Although cable 24 is illustrated with six optical fibers 26, anysuitable number of optical fibers may be incorporated within cable 24.For example, some embodiments may include up to twelve or twenty-fouroptical fibers in a unit. As one specific example, FIG. 5 is a schematiccross-sectional view of a fiber optic cable 24′ according to a secondembodiment of this disclosure. The cable 24′ of the second embodiment islike the cable 24 of the first embodiment, except for variations notedand variations that will be apparent to one of ordinary skill in theart. For example, in the cable 24′ of the second embodiment, strengthmaterial 28′ surrounds a group of optical fibers 26′, and a jacket 32′surrounds the strength material 28′ and a ripcord 30′.

Although the cable 24′ is illustrated with the group of optical fibers26′ including twelve optical fibers, any suitable number of opticalfibers (e.g., twenty-four optical fibers) may be incorporated within thecable 24′. The group of optical fibers 26′ has a dual-layer arrangementin that it includes an inner layer of optical fibers (e.g., three inneroptical fibers) and an outer layer of optical fibers (e.g., nine outeroptical fibers). In accordance with the second embodiment, the outerlayer of the optical fibers is positioned immediately adjacent to theinner layer of optical fibers, which may help to reduce the diameter ofthe cable 24′. For example and in accordance with the second embodiment,the strength material 28′ is not positioned between the inner and outerlayers of the optical fibers. As a result, when the cable 24′ is bent,the optical fibers therein may be relatively easily displaced to form aflattened configuration at the bend. When flattened, the optical fibersof the inner and outer layers may intermingle in a manner that seeks tominimize crushing forces and attenuation. Compactness stemming from thestrength material 28 not being positioned between the inner and outerlayers of the optical fibers may result in allowing the jacket 32′ toinclude a reduced amount of material without affecting a burn rating ofthe jacket. Alternatively, some of the strength material 28 may bepositioned between the inner and outer layers of the optical fibers.

The group of optical fibers 26′ may not be stranded, or it may bestranded as discussed above for the first embodiment. In addition and inaccordance with the second embodiment, the inner layer of optical fibersmay not be stranded or may be stranded with any of the lay lengthsdiscussed above for the group of optical fibers 26 of the firstembodiment, and the outer layer of optical fibers may not be stranded ormay be stranded around the inner layer of optical fibers with any of thelay lengths discussed above for the group of optical fibers 26 of thefirst embodiment.

In accordance with one aspect of the first and second embodiments ofthis disclosure, one or more of the above-discussed features seek toinhibit attenuation in a manner that allows for the jackets 32, 32′(FIGS. 1 and 5) to be relatively tight, without the tight jacketscausing excessive attenuation. For example, the jackets 32, 32′ may beextruded to a greater tightness than is typical in order to reduce theoverall size of the cables 24, 24′ and to reduce the amount of materialneeded for the jackets. A tight jacket may be applied by way of pressureextrusion, which causes the tight jacket to constrict against andcompress against the strength material. In this respect, the costsavings of using a tight jacket on a twelve-fiber indoor cable, forexample, may be about $2/km for riser cables and about $6/km for plenumcables. The jackets 32, 32′ being relatively tight is optional. That is,in some versions of the first and second embodiments, thetightness/looseness of the jackets 32, 32′ may be conventional. Whereashaving a tight jacket has some manufacturing advantages, having a tightjacket may cause increased optical attenuation because a tight jacketmay limit the movement of the optical fibers when the cable is bent,such as when the cable is wrapped around a mandrel or even when wrappedon a reel.

FIG. 6 is a chart illustrating differences between the intrinsic opticalattenuation of different types of optical fibers stranded in acomparative cable (not shown) with a relatively tight jacket. Thetightly-jacketed comparative cable is in some ways similar to the cable24′ (FIG. 5) of the second embodiment of this disclosure, except that inaddition to including four low attenuation optical fibers (i.e., “bendinsensitive” 50 μm multimode optical fibers that may be used in thegroups of optical fibers 26, 26′ of the first and second embodiments) itincludes four regular attenuation optical fibers (i.e., standard 50 μmmultimode optical fibers).

The chart of FIG. 6 shows the optical attenuation (or loss of light) indecibels per kilometer (dB/km) of light having a wavelength of 850 nm.FIG. 6 shows results 62 for the four low attenuation optical fibers ofthe tightly-jacketed comparative cable. FIG. 6 also shows results 64 forthe four regular attenuation optical fibers of the tightly-jacketedcomparative cable. Even with the tight jacket, it can be observed fromFIG. 6 that the four low attenuation optical fibers of thetightly-jacketed comparative cable exhibit lower intrinsic opticalattenuation than that exhibited by the four regular attenuation opticalfibers of the tightly-jacketed comparative cable.

FIG. 7 is a chart illustrating changes in optical attenuation thatoccurred when the tightly-jacketed comparative cable was wrapped fivetimes around a 16 mm mandrel. In FIG. 7, the first group of measurements72 and second group of measurements 74 represent the delta attenuationexhibited by the four low attenuation optical fibers of thetightly-jacketed comparative cable. In FIG. 7, the third and fourthgroups of measurements 76, 78 represent the delta attenuation exhibitedby the four regular attenuation optical fibers of the tightly-jacketedcomparative cable. The first and third groups of measurements 72, 76were made with 850 nm light transmitted through the tightly-jacketedcomparative cable. The second and fourth groups of measurements 74, 78were made with 1300 nm light transmitted through the tightly-jacketedcomparative cable.

Each of the cables 24, 24′ may be characterized as being a unit, and twoor more of the units may be combined into a single cable to providecables with higher fiber counts.

Throughout the foregoing disclosure, the adjective “about” has been usedin numerous locations preceding an amount. Other embodiments of thisdisclosure are like the above-discussed embodiments, except that theadjective “about” is optional and may be omitted.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention.

1. A fiber optic cable comprising: a plurality of optical fibers,wherein any lay length of the optical fibers is greater than or equal toabout 160 mm; strength material surrounding the plurality of opticalfibers, wherein any lay length of the strength material is greater thanor equal to about 130 mm; and a polymer jacket surrounding the strengthmaterial; wherein each of the optical fibers is configured to exhibit abend-induced optical attenuation of less than or equal to about 0.6 dBwhen wrapped one turn around a 7.5 mm mandrel.
 2. The fiber optic cableof claim 1, wherein the strength material comprises strength membersthat are substantially parallel to one another.
 3. The fiber optic cableof claim 1, wherein the strength material is stranded around theplurality of optical fibers, so that the lay length of the strengthmaterial is greater than or equal to about 500 mm.
 4. The fiber opticcable of claim 2, wherein the strength material has a lay length greaterthan or equal to about 1000 mm.
 5. The fiber optic cable of claim 1,wherein the plurality of optical fibers are substantially parallel toone another.
 6. The fiber optic cable of claim 1, wherein the pluralityof optical fibers is stranded, so that the lay length of the pluralityof optical fibers is greater than or equal to about 500 mm.
 7. The fiberoptic cable of claim 6, wherein the lay length of the plurality ofoptical fibers is greater than or equal to about 1000 mm.
 8. The fiberoptic cable of claim 1, wherein each of the optical fibers is configuredto exhibit a bend-induced optical attenuation of less than or equal toabout 0.2 dB when wrapped one turn around a 7.5 mm mandrel.
 9. The fiberoptic cable of claim 1, wherein each of the optical fibers is aconfigured to exhibit a bend-induced optical attenuation of less than orequal to about 0.08 dB when wrapped one turn around a 7.5 mm mandrel.10. The fiber optic cable of claim 1, wherein each of the optical fibersis tight buffered optical fiber.
 11. The fiber optic cable of claim 1,wherein the strength material comprises aramid fibers.
 12. A fiber opticcable comprising: a plurality of tight buffered optical fibers having alay length of greater than 160 mm; strength material surrounding theplurality of tight buffered optical fibers; and a polymer jacketsurrounding the strength material; wherein each of the tight bufferedoptical fibers is configured to exhibit a bend-induced opticalattenuation of less than or equal to about 0.6 dB when wrapped one turnaround a 7.5 mm mandrel.
 13. The fiber optic cable of claim 12, whereinthe plurality of tight buffered optical fibers are substantiallyparallel to one another.
 14. The fiber optic cable of claim 12, whereinthe lay length of the plurality of tight buffered optical fibers isgreater than or equal to about 500 mm.
 15. The fiber optic cable ofclaim 12, wherein each of the tight buffered optical fibers isconfigured to exhibit a bend-induced optical attenuation of less than orequal to about 0.2 dB when wrapped one turn around a 7.5 mm mandrel. 16.The fiber optic cable of claim 12, wherein each of the tight bufferedoptical fibers is configured to exhibit a bend-induced opticalattenuation of less than or equal to about 0.08 dB when wrapped one turnaround a 7.5 mm mandrel.
 17. The fiber optic cable of claim 12, whereinthe strength material comprises strength members that are substantiallyparallel to one another.
 18. The fiber optic cable of claim 12, whereinthe strength material has a lay length greater than or equal to about500 mm.
 19. The fiber optic cable of claim 12, wherein the strengthmaterial has a lay length greater than or equal to about 1000 mm. 20.The fiber optic cable of claim 19, wherein the strength materialcomprises aramid fibers.
 21. The fiber optic cable of claim 12, wherein:a first group of the tight buffered optical fibers resides within aninner layer and a second group of the tight buffered optical fibersresides within an outer layer; and the first group is immediatelyadjacent to the second group.
 22. The fiber optic cable of claim 12,wherein each of the tight buffered optical fibers exhibits an intrinsicoptical attenuation of less than or equal to about 3.0 dB/km.
 23. Thefiber optic cable of claim 12, wherein there are at least 24 of thetight buffered optical fibers in the fiber optic cable.
 24. A method ofmanufacturing a fiber optic cable, the method comprising: stranding aplurality of optical fibers with a lay length of greater than 160 mm,wherein each optical fiber exhibits a bend-induced attenuation of lessthan or equal to about 0.6 dB when wrapped one turn around a 7.5 mmmandrel; surrounding the plurality of optical fibers with strengthmaterial; and extruding a polymer jacket around the strength material.25. The method of claim 24, wherein the stranding of the optical fiberscomprises positioning at least one optical fiber within an inner layerand at least one optical fiber within an outer layer, and arranging theouter layer immediately adjacent to the inner layer.
 26. The method ofclaim 24, comprising performing the stranding, surrounding, andextruding at a line speed of at least 30 meters per minute.